1. Field of the Invention
This invention relates to automatic stop valves and particularly to pilot controlled automatic stop valves with manual reset for operation in liquid fluid environments such as hydraulic control systems.
In hydraulic control system operation, breakage or failure of an element in the fluid line, such as a conduit or a pump, may cause injury or damage if not promptly controlled. For example, fluid may be lost or may cause damage if not contained. Moreover, hydraulically controlled machinery may immediately become erratic threatening damage to equipment and injury to workers. A particular danger exists if fluid pressure is unexpectedly restored during maintenance or attempted operation. Absent adequate safety mechanisms, the hydraulic system may be actuated in an undesired mode which may also cause injury and damage. It is therefore desirable to provide adequate safety precautions to guard against damage to fluid systems and equipment and injury to workers.
2. Description of the Prior Art
Remote controlled shut-off valves are well known, particularly in pneumatic systems. Generally such valves include a diaphram separating chambers across which a pressure level may be monitored. If fluid pressure deviates outside preselected lower or upper limits, system operation is automatically terminated. Remote valve control permits valves to be reset to restore system operation.
Manually resettable pilot control valves are also known to the art. For example, U.S. Pat. No. 3,661,173 describes a control valve in which downstream back pressure is employed to balance the upstream pressure, the upstream pressure being employed to maintain a valve gate in an open position. The valve therein disclosed includes a flexible membrane defining a portion of the wall of a balancing chamber. Such membranes or diaphrams appear to be a common expedient in pilot controlled valves. Valves of the exemplary configuration are subject to failure due to the fatigue and possible breakdown of the membrane. The exemplary valve also appears to disclose a balancing chamber preferably of a constant volume separated by a significant fluid path distance from the valve aperture. Such features appear to be superfluous expedients in many applications.